Are the gate receipts so high that we need a new stadium to accomodate all ?
I don't know. Back in the early sixties when there was a derby match I used to hear things like "30,000 spectators in - 200,000 out" or "if we had the Maracana it would still be 200,000 locked out".
But nowadays teams settle for new stadiums of barely 30,000 capacity and they also think very highly of those new 30,000 stadiums. We do of course have television and internet now.
Why do you think a big stadium with 80,000-100,000 seats is needed ?